Quote from Ol' Yella:
The only thing I can think of is an emergency reverse split if something like that happened.
If the crash happened too fast for a reverse split to be done-- it would probably go to zero or 1 cent and then be split the next day.
I dont think it could go less than zero. An ETF cant have a negative value, can it?
In either case you would probably lose all your money. But at least its safer than futures, where in a bad enough crash you could end up owing money to your broker....